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Kinetics and mechanism of the interconversion of inverse bicontinuous cubic mesophases
This paper describes time-resolved x-ray diffraction data monitoring the transformation of one inverse bicontinuous cubic mesophase into another, in a hydrated lipid system. The first section of the paper describes a mechanism for the transformation that conserves the topology of the bilayer, based on the work of Charvolin and Sadoc, Fogden and Hyde, and Benedicto and O'Brien in this area. We show a pictorial representation of this mechanism, in terms of both the water channels and the lipid bilayer. The second section describes the experimental results obtained. The system under investigation was 2:1 lauric acid: dilauroylphosphatidylcholine at a hydration of 50% water by weight. A pressure-jump was used to induce a phase transition from the gyroid (Q(II)(G)) to the diamond (Q(II)(D)) bicontinuous cubic mesophase, which was monitored by time-resolved x-ray diffraction. The lattice parameter of both mesophases was found to decrease slightly throughout the transformation, but at the stage where the Q(II)(D) phase first appeared, the ratio of lattice parameters of the two phases was found to be approximately constant for all pressure-jump experiments. The value is consistent with a topology-preserving mechanism. However, the polydomain nature of our sample prevents us from confirming that the specific pathway is that described in the first section of the paper. Our data also reveal signals from two different intermediate structures, one of which we have identified as the inverse hexagonal (H-II) mesophase. We suggest that it plays a role in the transfer of water during the transformation. The rate of the phase transition was found to increase with both temperature and pressure-jump amplitude, and its time scale varied from the order of seconds to minutes, depending on the conditions employed
Ionic liquids that form adducts with alcohols
Ionic liquids bearing an activated carbonyl group in the cation are shown to form adducts with alcohols without the aid of any catalysts. How these functionalised ionic liquids could be used in altering vapour phase compositions of alcohols and in alcohol separations are demonstrated.</p
Engineering swollen cubosomes using cholesterol and anionic lipids
Dispersions of non-lamellar lipid membrane assemblies are gaining increasing interest for drug delivery and protein therapeutic application. A key bottleneck has been the lack of rational design rules for these systems linking different lipid species and conditions to defined lattice parameters and structures. We have developed robust methods to form cubosomes (nanoparticles with a porous internal structure) with water channel diameters of up to 171 Å which are over 4 times larger than archetypal cubosome structures. The water channel diameter can be tuned via the incorporation of cholesterol and the charged lipids DOPA, DOPG or DOPS. We have found that large molecules can be incorporated into the porous cubosome structure and these molecules can interact with the internal cubosome membrane. This offers huge potential for accessible encapsulation and protection of biomolecules, and development of confined interfacial reaction environments
Calculation of the Phase Behavior of Lipids
The self-assembly of monoacyl lipids in solution is studied employing a model
in which the lipid's hydrocarbon tail is described within the Rotational
Isomeric State framework and is attached to a simple hydrophilic head.
Mean-field theory is employed, and the necessary partition function of a single
lipid is obtained via a partial enumeration over a large sample of molecular
conformations. The influence of the lipid architecture on the transition
between the lamellar and inverted-hexagonal phases is calculated, and
qualitative agreement with experiment is found.Comment: to appear in Phys.Rev.
CASTNet: Community-Attentive Spatio-Temporal Networks for Opioid Overdose Forecasting
Opioid overdose is a growing public health crisis in the United States. This
crisis, recognized as "opioid epidemic," has widespread societal consequences
including the degradation of health, and the increase in crime rates and family
problems. To improve the overdose surveillance and to identify the areas in
need of prevention effort, in this work, we focus on forecasting opioid
overdose using real-time crime dynamics. Previous work identified various types
of links between opioid use and criminal activities, such as financial motives
and common causes. Motivated by these observations, we propose a novel
spatio-temporal predictive model for opioid overdose forecasting by leveraging
the spatio-temporal patterns of crime incidents. Our proposed model
incorporates multi-head attentional networks to learn different representation
subspaces of features. Such deep learning architecture, called
"community-attentive" networks, allows the prediction of a given location to be
optimized by a mixture of groups (i.e., communities) of regions. In addition,
our proposed model allows for interpreting what features, from what
communities, have more contributions to predicting local incidents as well as
how these communities are captured through forecasting. Our results on two
real-world overdose datasets indicate that our model achieves superior
forecasting performance and provides meaningful interpretations in terms of
spatio-temporal relationships between the dynamics of crime and that of opioid
overdose.Comment: Accepted as conference paper at ECML-PKDD 201
Surface nanobubbles as a function of gas type
We experimentally investigate the nucleation of surface nanobubbles on
PFDTS-coated silicon as a function of the specific gas dissolved in the water.
In each case we restrict ourselves to equilibrium conditions (,
). Not only is nanobubble nucleation a strong
function of gas type, but there also exists an optimal system temperature of
where nucleation is maximized, which is weakly
dependent on gas type. We also find that contact angle is a function of
nanobubble radius of curvature for all gas types investigated. Fitting this
data allows us to describe a line tension which is dependent on the type of
gas, indicating that the nanobubbles are sat on top of adsorbed gas molecules.
The average line tension was
New type of microengine using internal combustion of hydrogen and oxygen
Microsystems become part of everyday life but their application is restricted
by lack of strong and fast motors (actuators) converting energy into motion.
For example, widespread internal combustion engines cannot be scaled down
because combustion reactions are quenched in a small space. Here we present an
actuator with the dimensions 100x100x5 um^3 that is using internal combustion
of hydrogen and oxygen as part of its working cycle. Water electrolysis driven
by short voltage pulses creates an extra pressure of 0.5-4 bar for a time of
100-400 us in a chamber closed by a flexible membrane. When the pulses are
switched off this pressure is released even faster allowing production of
mechanical work in short cycles. We provide arguments that this unexpectedly
fast pressure decrease is due to spontaneous combustion of the gases in the
chamber. This actuator is the first step to truly microscopic combustion
engines.Comment: Paper and Supplementary Information (to appear in Scientific Reports
Tuberculous meningitis in children: a forgotten public health emergency
Tuberculous meningitis (TBM) remains a major cause of morbidity and mortality in children with tuberculosis (TB), yet there are currently no estimates of the global burden of paediatric TBM. Due to frequent non-specific clinical presentation and limited and inadequate diagnostic tests, children with TBM are often diagnosed late or die undiagnosed. Even when diagnosed and treated, 20% of children with TBM die. Of survivors, the majority have substantial neurological disability with significant negative impact on children and their families. Surveillance data on this devastating form of TB can help to quantify the contribution of TBM to the overall burden, morbidity and mortality of TB in children and the epidemiology of TB more broadly. Paediatric TBM usually occurs shortly after primary infection with Mycobacterium tuberculosis and reflects ongoing TB transmission to children. In this article we explain the public health importance of paediatric TBM, discuss the epidemiology within the context of overall TB control and health system functioning and the limitations of current surveillance strategies. We provide a clear rationale for the benefit of improved surveillance of paediatric TBM using a TB care cascade framework to support monitoring and evaluation of paediatric TB, and TB control more broadly. Considering the public health implications of a diagnosis of TBM in children, we provide recommendations to strengthen paediatric TBM surveillance and outline how improved surveillance can help us identify opportunities for prevention, earlier diagnosis and improved care to minimize the impact of TBM on children globally
Adhesion between oppositely-charged polyelectrolytes
The adhesion between a grafted polyelectrolyte layer (brush) and a gel of an oppositely charged polyelectrolyte has been measured as a function of applied pressure, and the interface has been traced using neutron reflectometry. The interface (in aqueous medium at pH 6) between the (polycationic) brush and the (polyanionic) gel has a limited pressure-dependence, with a small amount of deformation of the interface at the brush-gel contact. Brushes with a dry thickness of up to 13 nm exhibit weak adhesion (measured using a mechanical force tester) with an adhesive failure when the gel is detached. Thicker brushes result in the gel exhibiting cohesive failure. Reversing the geometry, whereby a polycationic brush is replaced with a polyanion and the polyanionic gel is replaced with a polycation reveals that the pH-dependence of the adhesion is moderately symmetric about pH 6, but that the maximum force required to separate the polycation gel from the polyanion brush over the range of pH is greater than that for the polycation brush and polyanion gel. The polyanion used is poly(methacrylic acid) (PMAA) and polycations of poly[2-(diethyl amino)ethyl methacrylate] (PDEAEMA) and poly[2-(dimethyl amino)ethyl methacrylate] (PDMAEMA) were used
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